As disclosed in U.S. Pat. No. 4,337,091 to El-Shazly and Baker, a substantial body of literature has developed in recent years pertaining to the electroless or autocatalytic deposition of gold on surfaces, both metallic and non-metallic. As to the treatment of non-metallic surfaces, e.g., glass, it has been essential to subject the substrate to extensive precleaning followed by a special activation treatment prior to the gold plating operation. See, for example, U.S. Pat. No. 4,091,128 to Franz and Vanek where gold is being plated on glass and the precleaning and activation treatments are required and described in great detail. Particular reference is made to the prior patents to Miller: U.S. Pat. Nos. 3,457,138 and 3,723,158. Precleaning and activation treatments are also prescribed in U.S. Pat. No. 4,162,337 to D'Asaro and Okinaka which pertains to a process for making III-V semiconductor devices with electroless gold plated layers. A wide variety of precleaning methods can be employed. This step generally involves removing oxide contaminants from the surface of the substrate. Various mechanical means, i.e. rubbing the surface, and chemical means, i.e. acid rinses have been proposed and are disclosed in the Franz et al. and D'Asaro patents referred to above.
Surfaces of non-metallic substrates, have been rendered catalytically active by producing a film of catalytic particles thereon. This may be done by the method described in U.S. Pat. No. 3,589,916 upon such surfaces as glass, ceramics, various plastics, etc. When a plastic substrate was plated, it was initially etched, preferably in a solution of chromic and sulfuric acid. After rinsing, the substrate was immersed in an acidic solution of stannous chloride, such as stannous chloride and hydrochloric acid, rinsed with water and then contacted with an acid solution of a precious metal, such as paladium chloride in hydrochloric acid. The now catalytically active non-metallic substrate was subsequently contacted with the electroless plating solutions. When the substrate to be gold plated is a metallized ceramic utilizing, for example, tungsten, molybdenum, electroless nickel, and copper substrates, severe pretreatments such as sintering at high temperatures in a reducing atmosphere have been prescribed. Attention is directed to the article entitled "Electroplating of Gold and Rhodium" by Levy, Arnold and Ma in Plating and Surface Finishing, pages 104-107 (May, 1981). The author's set forth details concerning various procedures for pretreatment of the molybdenum substrate.
U.S. Pat. No. 3,862,850 to Trueblood deals with electroless gold plating of refractory metals, including wherein powders of the refractory metals are sintered to ceramic insulators and subsequently gold plated to allow their brazing to metal members or in certain electronic operations the refractory powders overplated with gold act as electrical conductors on ceramic substrates. The plating of tungsten metallized ceramic circuit boards is illustrated in column 3, while the gold plating of molybdenum metal is illustrated in column 4. In each instance, however, Trueblood requires an elaborate precleaning, also referred to as an activation treatment, that requires soaking the metal in a hot alkaline descaler, rinsing in deionized water, further rinsing in hot dilute acid solution, and then a final rinsing step using boiling deionized water.
Trueblood's electroless gold plating bath consists essentially of (1) water, (2) potassium or sodium gold cyanide, (3) organic chelating agent, (4) non-ammonical alkali metal salt of a weak acid, and (5) a non-ammonical alkali metal hydroxide.
It obviously would be advantageous to minimize the extensive pretreatment requirements and to avoid the need of a special activation treatment which is generally employed after precleaning in the prior art processes.